The tie-up between the largest US automaker and Tokyo- based Honda is to include exchanging engineers, joint use of research facilities and shared sourcing of parts and materials, they said today in a joint statement. The goal is a common hydrogen powertrain to make the vehicles more affordable, they said, without providing price or investment details.

“We are convinced this is the best way to develop this important technology,” GM Chief Executive Officer Dan Akerson said in the statement. Such vehicles can help curb petroleum dependence and underpin sustainable mobility, he said.

The allure of hydrogen as a clean automotive fuel led carmakers a decade ago – notably the former General Motors – to predict millions of fuel-cell autos would be on the road by now. While a mass market for hydrogen cars may be a decade or more away, the enticement is undiminished.

Toyota, which had a hydrogen technology alliance with GM in the early 2000s, plans to release a fuel- cell sedan in the 2015 model year that will be unveiled in November. Honda, Hyundai and Daimler’s Mercedes- Benz also plan retail sales of hydrogen cars in 2015, and Bayerische Motoren Werke has said it intends to use Toyota’s fuel-cell system.

Environmental rules in the US, Europe and Japan encourage automakers to sell vehicles that don’t emit climate-warming gases. That has aided hybrid sales, led to lighter cars and smaller engines, and convinced Tesla Motors and Nissan to push high-volume sales of battery cars.

“Among all zero CO2 emission technologies, fuel-cell electric vehicles have a definitive advantage with range and refueling time that is as good as conventional gasoline cars,” Honda President Takanobu Ito said in the statement.

GM and Honda also they’ll jointly lobby for an expanded network of hydrogen fuel stations, now currently clustered in the US, mainly in California.

Battery-electric cars such as Tesla’s Model S and Nissan’s Leaf hatchback share technologies with fuel-cell cars, including similar electric motors to power the wheels, brakes that capture power when stopping, software and related electronics.

The difference is the electricity source. Battery cars store it in large lithium-ion packs – Tesla’s weigh 1,000 pounds (454 kilograms). Fuel cells generate it in an electro- chemical reaction of hydrogen and air.

In a fuel cell, hydrogen gas passes through a stack of plastic membranes and metal plates – like syrup soaking a tower of platinum-dusted pancakes – to produce electricity.

Because of the precious metals needed, fuel-cell stacks remain expensive, as do high-pressure hydrogen tanks. Prototypes have cost $1 million to make.